Messages in this thread | | | Date | Wed, 28 Oct 2020 10:03:49 +0000 | From | Marc Zyngier <> | Subject | Re: [PATCH v3] KVM: arm64: ARM_SMCCC_ARCH_WORKAROUND_1 doesn't return SMCCC_RET_NOT_REQUIRED |
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On 2020-10-26 13:25, Will Deacon wrote: > On Fri, Oct 23, 2020 at 08:47:50AM -0700, Stephen Boyd wrote: >> According to the SMCCC spec[1](7.5.2 Discovery) the >> ARM_SMCCC_ARCH_WORKAROUND_1 function id only returns 0, 1, and >> SMCCC_RET_NOT_SUPPORTED. >> >> 0 is "workaround required and safe to call this function" >> 1 is "workaround not required but safe to call this function" >> SMCCC_RET_NOT_SUPPORTED is "might be vulnerable or might not be, who >> knows, I give up!" >> >> SMCCC_RET_NOT_SUPPORTED might as well mean "workaround required, >> except >> calling this function may not work because it isn't implemented in >> some >> cases". Wonderful. We map this SMC call to >> >> 0 is SPECTRE_MITIGATED >> 1 is SPECTRE_UNAFFECTED >> SMCCC_RET_NOT_SUPPORTED is SPECTRE_VULNERABLE >> >> For KVM hypercalls (hvc), we've implemented this function id to return >> SMCCC_RET_NOT_SUPPORTED, 0, and SMCCC_RET_NOT_REQUIRED. One of those >> isn't supposed to be there. Per the code we call >> arm64_get_spectre_v2_state() to figure out what to return for this >> feature discovery call. >> >> 0 is SPECTRE_MITIGATED >> SMCCC_RET_NOT_REQUIRED is SPECTRE_UNAFFECTED >> SMCCC_RET_NOT_SUPPORTED is SPECTRE_VULNERABLE >> >> Let's clean this up so that KVM tells the guest this mapping: >> >> 0 is SPECTRE_MITIGATED >> 1 is SPECTRE_UNAFFECTED >> SMCCC_RET_NOT_SUPPORTED is SPECTRE_VULNERABLE >> >> Note: SMCCC_RET_NOT_AFFECTED is 1 but isn't part of the SMCCC spec >> >> Cc: Andre Przywara <andre.przywara@arm.com> >> Cc: Steven Price <steven.price@arm.com> >> Cc: Marc Zyngier <maz@kernel.org> >> Cc: stable@vger.kernel.org >> Link: https://developer.arm.com/documentation/den0028/latest [1] >> Fixes: c118bbb52743 ("arm64: KVM: Propagate full Spectre v2 workaround >> state to KVM guests") >> Signed-off-by: Stephen Boyd <swboyd@chromium.org> >> --- >> >> I see that before commit c118bbb52743 ("arm64: KVM: Propagate full >> Spectre v2 workaround state to KVM guests") we had this mapping: >> >> 0 is SPECTRE_MITIGATED >> SMCCC_RET_NOT_SUPPORTED is SPECTRE_VULNERABLE >> >> so the return value '1' wasn't there then. Once the commit was merged >> we >> introduced the notion of NOT_REQUIRED here when it shouldn't have been >> introduced. >> >> Changes from v2: >> * Moved define to header file and used it >> >> Changes from v1: >> * Way longer commit text, more background (sorry) >> * Dropped proton-pack part because it was wrong >> * Rebased onto other patch accepted upstream >> >> arch/arm64/kernel/proton-pack.c | 2 -- >> arch/arm64/kvm/hypercalls.c | 2 +- >> include/linux/arm-smccc.h | 2 ++ >> 3 files changed, 3 insertions(+), 3 deletions(-) >> >> diff --git a/arch/arm64/kernel/proton-pack.c >> b/arch/arm64/kernel/proton-pack.c >> index 25f3c80b5ffe..c18eb7d41274 100644 >> --- a/arch/arm64/kernel/proton-pack.c >> +++ b/arch/arm64/kernel/proton-pack.c >> @@ -135,8 +135,6 @@ static enum mitigation_state >> spectre_v2_get_cpu_hw_mitigation_state(void) >> return SPECTRE_VULNERABLE; >> } >> >> -#define SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED (1) >> - >> static enum mitigation_state >> spectre_v2_get_cpu_fw_mitigation_state(void) >> { >> int ret; >> diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c >> index 9824025ccc5c..25ea4ecb6449 100644 >> --- a/arch/arm64/kvm/hypercalls.c >> +++ b/arch/arm64/kvm/hypercalls.c >> @@ -31,7 +31,7 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu) >> val = SMCCC_RET_SUCCESS; >> break; >> case SPECTRE_UNAFFECTED: >> - val = SMCCC_RET_NOT_REQUIRED; >> + val = SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED; >> break; >> } >> break; >> diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h >> index 15c706fb0a37..0e50ba3e88d7 100644 >> --- a/include/linux/arm-smccc.h >> +++ b/include/linux/arm-smccc.h >> @@ -86,6 +86,8 @@ >> ARM_SMCCC_SMC_32, \ >> 0, 0x7fff) >> >> +#define SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED 1 > > I thought we'd stick this in asm/spectre.h, but here is also good: > > Acked-by: Will Deacon <will@kernel.org>
Acked-by: Marc Zyngier <maz@kernel.org>
Will, if you're about to send fixes to Linus, can you please pick this one up?
M. -- Jazz is not dead. It just smells funny...
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